The invention relates to an exhaust gas system for an internal combustion engine and to methods for operating the exhaust gas system.
German laid-open specification DE 10 2009 032 213 A1, for example, discloses an exhaust gas system of an internal combustion engine, with a first exhaust tract assigned to a first group of cylinders of the internal combustion engine and with a second exhaust tract assigned to a second group of cylinders of the internal combustion engine. Each exhaust tract has a respective exhaust gas purification device and a first muffler arranged downstream of the respective exhaust gas purification device and also a second muffler arranged downstream of the respective first muffler, and an exhaust tailpipe arranged downstream of the respective second muffler.
A disadvantage of this known prior art is that the muffling resonator of the muffler is not variably adjustable.
Furthermore, the prior art has in general disclosed mufflers for exhaust gas systems which operate according to the absorption and/or reflection principle. The development of such a muffler generally means finding the best possible compromise between outlet noise (loudness downstream of the exhaust gas system tailpipe), exhaust gas backpressure and required muffler volume. In order to bypass such a compromise solution, mufflers are frequently designed with one or more movable closure elements or shut-off members, such as, for example, an exhaust gas flap, in order to permit different flow paths in the exhaust pipe of the muffler system. In the case of muffler systems for internal combustion engines, two, three or even four exhaust gas system tailpipes are frequently provided. In the muffler embodiments known from the prior art, the arrangement of the closure elements disadvantageously leads to exhaust gas no longer flowing through all of the exhaust gas system tailpipes or tailpipe branching elements, depending on the position of the closure element.
However, this prior art has the following disadvantages:
1) Customer irritation since exhaust gas does not emerge from all of the exhaust gas system tailpipes (visible at a lower outside temperature and by way of the different degree of soiling of the visible tailpipes);
2) High exhaust gas backpressure by means of a bottleneck in the exhaust gas system tailpipe;
3) Flow noises because of a bottleneck in the exhaust gas system tailpipe;
4) Thermal stress between cold and hot exhaust gas system tailpipe (risk of cracking);
5) Complicated routing of the muffling pipes in the muffler system;
6) High weight of the muffler system;
7) High production costs of the muffler system;
8) Flaps customarily can be switched separately or offset in time only to a limited extent; this results in a significant rise in exhaust gas backpressure in an exhaust tract.
It is the object of the present invention to avoid the abovementioned disadvantages and at the same time to introduce variability in the muffling properties of the muffler system.
This and other objects are achieved by providing an exhaust gas system, and method of operating same, for an internal combustion engine having at least one first and one second cylinder, wherein the first cylinder is assigned a first exhaust pipe and the second cylinder is assigned a second exhaust pipe, and wherein the first exhaust pipe is assigned a first muffler and the second exhaust pipe is assigned a second muffler. A first muffling pipe branches off from the first exhaust pipe upstream of a first shut-off member. The muffling pipe is guided through the first muffler and leads into the second exhaust pipe downstream of a second shut-off member. A second muffling pipe branches off from the second exhaust pipe upstream of the second shut-off member. The muffling pipe is guided through the second muffler and leads into the first exhaust pipe downstream of the first shut-off member.
All of the abovementioned problems are avoided by the configuration according to the invention of the exhaust gas system. The exhaust gas system has an advantageous construction with regard to the exhaust gas backpressure. By way of the construction according to the invention, one or both shut-off members can be closed, even simultaneously, without a substantial increase in the exhaust gas backpressure. In comparison to conventional exhaust gas systems, when shut-off members, such as, for example, exhaust gas flaps, are open, throttling (raising of the exhaust gas backpressure) is minimal or scarcely measurable since the entire volume of the exhaust pipe and muffling pipe as far as the end of the exhaust gas system is used. By way of a somewhat changed construction, the shut-off members can also be switched in a temporarily offset manner in order to improve a subjective audible impression during the switching phase. By way of the offset switching over of the two shut-off members, conspicuous acoustic jumps in level can be reduced in an advantageous manner.
With regard to power and dynamics (response behavior of the internal combustion engine), the exhaust gas backpressure, which is very low because of the configuration according to the invention, of the exhaust gas system has a highly positive effect. For slight acoustic adaptations, the volumes of the first muffler and of the second muffler can also be changed retrospectively. In addition, one or more possibly required resonators can be integrated in a simple manner into the exhaust gas system without a great outlay and while maintaining the symmetry.
Furthermore, the muffler can be constructed in a highly favorable manner by way of the symmetrical construction of the exhaust gas system.
A multiplicity of components of the exhaust gas system can be manufactured or used as favorable identical parts.
The muffler housing can be realized, for example, as a cost-effective wound muffler or in a shell construction. In the event of a realization as a wound muffler, the two side parts can be designed as identical parts. In the shell construction, the upper shell and the lower shell can each be designed as an identical part.
The exhaust pipes (FIG. 1, region a) can be produced and installed as identical components.
The Y branching elements from the exhaust pipes to the muffling pipes (FIG. 1, region b as far as/after the shut-off member) can be realized, for example, as a part molded by hydroforming. The latter can therefore be used as an identical part upstream and downstream of the shut-off member and on both sides of the mufflers.
The tailpipe branching elements are likewise to be as per the pipe branching (FIG. 1, region c). The tailpipe branching elements can likewise be designed as an identical part for both sides.
The muffling pipes with perforations and which are guided through the muffler (FIG. 1, region d) can likewise be realized as identical parts.
Should a resonator be required, the required partitions for both sides can likewise be realized as an identical part.
For the production, it is also possible to save on assembly tools because of the identical parts for the exhaust gas system. Depending on how the production of a manufacturer or supplier is realized, the identical assembly apparatus can be used for the preassembly of the Y branching elements and the shut-off members for both sides of the exhaust gas system.
All of the abovementined points lead to a significant reduction in the tool and production costs for the exhaust gas system according to the invention.
In addition, a possibly desirable lightweight construction can be realized significantly more simply by use of the large portion of identical parts and the reduction in variants of individual parts.
In a further development, the first and second mufflers may be arranged in a common housing. Further, the first muffling pipe may be assigned a first resonator chamber and the second muffling pipe may be assigned a second resonator chamber. Moreover, the first and second resonator chambers may be integrated into the common housing.
With the method for operating an exhaust gas system for an internal combustion engine according to the invention, minimum muffling is achieved by opening the first and second shut-off members.
With the method for operating an exhaust gas system for an internal combustion engine according to the invention, medium muffling is achieved by opening the first shut-off member and closing the second shut-off member.
With the method for operating an exhaust gas system for an internal combustion engine according to the invention, maximum muffling is achieved by closing the first and second shut-off members.
An exhaust gas system according to the invention and three methods for operating the exhaust gas system according to the invention are explained in more detail below in four figures.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.